3.2 Cylinder & Piston clearance spec & "wear limit" question

RogueEngineer · RogueEngineer's Garage

I'm currently taking piston diameter and cylinder bore measurements of an '85 3.2 Carrera engine I've torn apart. Cylinders appear to be the Mahle nikasil type. Odometer said 263k before I tore everything down. History unknown.

The spec, according to Wayne's book, details a 0.025-.042mm (.001-.0017") piston cylinder clearance. I'm currently clocking in at 0.05-.064mm (.002-.0025") clearance across all 6 p & c's. The extra clearance appears to be coming from the cylinders and not the pistons.

Wayne's book also has a note that says "A cylinder is worn if the dimension recorded is greater than the installation diameter by 0.08mm (.003")." Do i interpret this note as an "acceptable tolerance" window of +.08mm over the "new" spec listed in Wayne's book? Of course, if i was closer to that loose end of the window, It probably wouldn't be recommended to re-use.

I'm trying to determine what my path forward with these components will be. My instinct is telling me that these components are in the middle of their life and will be fine to hone (scotch brite), re-ring, and use.

What are everyone's thoughts?

Solamar · 12-23-2019, 06:54 PM

I asked a very reputable builder a similar question when I was building my 3.2 (I asked him to measure my p&cs to check if they were in tolerance). His response was that 3.2 Mahle Nikisil p&cs are almost never worn out of spec and to just check ring gap.

Just a point of reference for you.

targa72e · 12-24-2019, 11:54 AM

How are all the other important measurements. Ovality, taper and ring gap?

John

r lane · 12-24-2019, 05:14 PM

If the cylinder is still round, put in new rings and go. Another path is to have them refinished. Done with Nikasil and you have new cylinders. There are a number of companies around that do that. Bob

Trackrash · Trackrash's Garage

Round and taper measurements are key with the cylinders.

An experienced builder friend of mine looks at the cross hatch. If it is even throughout the cylinder, meaning it still exists at the top of the ring's stroke, you are probably OK.